Telecommunications test sets are used for a variety of tests, including the measurement of resistances, checking the continuity or discontinuity of a circuit, and monitoring the status of a telephone line. When wires are being installed or serviced, there is often more than one technician performing the task. Often, there is no convenient electrical power available to the technician at the job site. To solve the power problem and to help the technicians accomplish their tasks, many test sets are battery powered and have the ability to provide power for communication between remote locations over existing wires, provided that the wires are not currently used for other purposes. If the wire are in use, damage to the test set may result.
If the wires are available for communication between the technicians, the technicians connect their telephone sets (commonly called butt sets) to the wires. Power is provided for the telephone sets by the test set. Typically, the test set simply provides a voltage in series with a current limiting resistor. This circuit arrangement provides limited power for communications, resulting in weak signals at the telephone sets and a practical limit of powering two telephone sets.
It will, therefore, be appreciated that there is a significant need for a portable, battery powered telecommunications test set that will not be damaged if connected to active lines and has the capability of providing power for as many as four telephone sets.